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The Effects of tDCS on Intermuscular Coherence During Speaking in Healthy Younger and Older Adults

  • Author / Creator
    Feil, Althea
  • Background. Research in neuroplasticity has focused recently on the preservation of cognitive and motor functions in aging adults. Previous studies have shown that non-invasive neurostimulation can mitigate age-related changes in speech motor control. Specifically, transcranial direct current stimulation (tDCS) has been shown to improve performance on cognitive, language, and motor tasks in older adults. For example, anodal tDCS over Broca’s area increases speech rate and articulatory accuracy during recitation of tongue twisters. tDCS can be delivered off-line (before a task) or on-line (during a task), which results in differential changes in underlying neural mechanisms. Little is known about off-line tDCS and neuromodulation of speech motor control in typically aging adults. Methods. Thirty healthy younger adults (18-43yrs) and 30 healthy older adults (54-77yrs) recited tongue twisters pre- and post-13 minutes (1mA) tDCS over Broca’s area (FC5-10/20 system). Participants were randomly assigned to receive anodal, cathodal, or sham stimulation. Effects on intermuscular coherence between perioral muscles and intercostal and oblique chest wall muscles were evaluated. Results. tDCS did not modulate the strength of perioral or chest wall intermuscular coherence in either younger or older adults. However, tDCS influenced where the peak coherence frequency occurred, the lag or timing between motor unit firing of paired muscles and the overall similarity between paired muscle signals. Only one significant anode and cathode post-stimulation effect (i.e., timing of motor unit firing) was found for the perioral muscles in older adults. Based on individual responses and group data analyses, it appears that most of the modulatory effects were found for chest wall muscles following cathodal tDCS. Cathodal tDCS appeared to affect where peak coherence frequencies occurred, timing of motor unit firing as well as similarity between intercostal and oblique muscle signals. Whereas these effects were observed primarily in the high frequency bandwidth (i.e., 60-110 Hz) the patterns of post-cathodal tDCS changes appeared to be age dependent. Conclusion. Strength of coherence (i.e., peak coherence amplitude) remained stable pre-post stimulation for both younger and older adults. The significant effects on measures of peak coherence frequency, cumulant density (lag) and cross-correlation coefficient (similarity) indicate that these measures may be more sensitive to stimulation than peak coherence amplitude. Additionally, the significant modulatory effects found for cathodal stimulation add to the body of literature examining long-term-depression like effects of tDCS. The results of this study expand our understanding of the effects of off-line tDCS on intermuscular coherence of perioral and chest wall muscles during a highly complex speech motor control task (i.e., tongue twisters) in younger and older adults. The results may help guide future studies examining the effects of tDCS on intermuscular coherence in healthy adults.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-sx07-zy85
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.